The present invention pertains to a method for measuring ink density in a printing machine.
A device for measuring ink density in a running printing machine has been disclosed in DE-OS No. 20 23 467. This device includes a measuring head, a light source for the illumination of measuring marks provided on a sheet being printed, and a photometer which receives reflected light. In the disclosed device the information is obtained by the comparison of the ink density on all printed sheets, and an assumption is made on the basis of that information for controlling an inking.
An essential structural component of the known device is the photometer with a response time in the range of milliseconds. With such response time a minimal length of the measuring mark (in the printing direction) of about 5 mm is realized at the speed of the upper surface of the printed sheet of about 2 m/s.
The measuring value is constituted in the known device by a timely integration. The disadvantage of this known device is the dependence of the precision of measuring on the speed of the printed sheet because, due to a high response time of one millisecond, various large surfaces of the measuring marks are monitored. A further disadvantage of the known device is that a medium precision for satisfactory controlling the inking is insignificant.